The state of the art as concerns the manufacture of long life high current density cathodes involves the initial mixing and heating of barium carbonate, BaCO.sub.3 calcium carbonate, CaCO.sub.3 and aluminum oxide, Al.sub.2 O.sub.3. The BaCO.sub.3 and CaCO.sub.3 are decomposed at 1450.degree. C. to form BaO and CaO that react with the Al.sub.2 O.sub.3 to form aluminates. The aluminates are then impregnated into a porous billet of tungsten, or tungsten and iridium, or tungsten and osmium or tungsten and rhodium, etc., heated in a cathode environment, and testing made. The process involves the decomposition of the aluminates to form the barium iridiates, barium osmiates, and barium rhodiates.
In Ser. No. 204,327, an improved method of making a long life high density cathode is described and claimed in which the intermediate formation of aluminates is obviated and in which lower temperatures can be used. In the method of Ser. No. 204,327 a barium peroxide containing material is used as the impregnant. More particularly, according to the Ser. No. 204,327 method, a suitable porous billet of tungsten, or tungsten-iridium, or tungsten-osmium or tungsten-rhodium is impregnated with a barium peroxide containing material in a hydrogen atmosphere and slowly heated to above 800.degree. C. to decompose the barium peroxide, BaO.sub.2 to form barium oxide, BaO and oxygen O.sub.2 according to the reaction: EQU 2BaO.sub.2 .fwdarw.2BaO+O.sub.2
The sample BaO reacts with the tungsten wall of the billet or the tungsten-rhodium wall of the billet to form the desired oxyanion.
Though the Ser. No. 204,327 method is desirable, it would be of further advantage in the manufacture of a long life high current density cathode to use even lower temperatures in the impregnation of the tungsten-iridium billet.